We are investigating the role of tumor suppressor genes in the pathogenesis of human cancer. Our recent findings are as follows: 1) we have examined 130 lung cancer samples for inactivation of the retinoblastoma (RB) gene and have determined that 90-95% of small cell lung cancer and 15-20% of non-small cell lung cancer have homozygous mutations within this gene. We are completing a correlation of this data with clinical outcome and drug sensitivity testing to determine if RB testing offers prognostic information for patients with lung cancer; 2) using information obtained from our previous analyses of in vivo RB mutant proteins, we have constructed a series of in vitro mutations within the RB protein to define amino acid residues that are critical for RB function; 3) using RB fusion proteins as a reagent to molecularly clone RB-binding proteins, we have identified the interaction of the RB protein with a nuclear matrix product; 4) we have also studied the expression of another RB-binding protein (designated RBP- 1) and have determined that it undergoes extensive alternative exon processing that modulates its interactions with the cell-cycle regulator, p34cdc2. We have also raised specific antisera against this 200kDa binding protein and are examining its biologic activity on cell growth. 5) we have successfully expressed RB protein in lung tumors and have observed suppression of tumorigenicity in nude mice. We have also observed that we can reverse the "tumor suppressor" effect with extracts enriched in extracellular matrix (ECM), and we are currently examining how ECM and RB pathways might interact. 6) in collaboration with Dr. Crystal (NHLBI), we have constructed a series of retroviral and adenoviral constructs containing the open reading frames of RB and p53. Finally, we plan to use these vectors to determine the feasibility of in vivo tumor suppression in animal models.